Method for generating hydraulic power in an aircraft, use of a hybrid power control unit and drive system

ABSTRACT

A method for generating hydraulic power in an aircraft, the aircraft having a drive system comprising at least one transmission shaft connected to a power control unit, the power control unit having an electric motor and a hydraulic displacement machine connected to a differential gear unit for driving a common output shaft. The method includes switching the hydraulic displacement machine into a pump mode, arresting the output shaft, rotating the electric motor such that the hydraulic displacement machine is driven due to the arrested output shaft and supplying the fluid flow into a hydraulic system. A drive system of an aircraft may thereby be used for either moving control surfaces or for generating hydraulic power in an aircraft. This hydraulic power may be used to cover hydraulic load peaks during aircraft operation or to power hydraulic devices without the need of additional hydraulic power generation components.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to European Patent Application No. 12178 041.5, filed Jul. 26, 2012, and to U.S. Provisional PatentApplication No. 61/675,853, filed Jul. 26, 2012, which are eachincorporated herein by reference in their entirety.

TECHNICAL FIELD

The technical field relates to a method for generating hydraulic powerin an aircraft, the aircraft having a drive system comprising at leastone transmission shaft connected to a hybrid power control unit, the useof a hybrid power control unit and a drive system comprising at leastone transmission shaft connected to a hybrid power control unit.

BACKGROUND

In an aircraft, hydraulic power is usually generated by engine drivenhydraulic pumps connected to two or more hydraulic line systems. For thepurpose of increasing the redundancy or the capability of compensatingload peaks in the hydraulic power demand, additional hydraulic pumps maybe provided driven by dedicated electric motors.

Main hydraulic loads in an aircraft are hydraulic actuators connected tocontrol surfaces such as ailerons, elevons and rudders, as well aslanding gear actuators and cargo door actuators. During start andlanding phases, high lift systems are commonly used for increasing thelift coefficient of the aircraft. Typically, high lift systems ofcommercial and military aircraft are powered by a drive system with acentral power control unit (PCU), wherein the PCU may include at leastone hydraulic motor.

Other objects, desirable features and characteristics will becomeapparent from the subsequent summary and detailed description, and theappended claims, taken in conjunction with the accompanying drawings andthis background.

SUMMARY

Each hydraulic pump and each electric motor installed in the aircraftfor driving a hydraulic pump increases the total weight of the aircraft.Accordingly, it may be desirable to provide a method and a system forgenerating hydraulic power with a sufficient redundancy and reducing theresulting weight at the same time.

According to various exemplary embodiments, a method for generatinghydraulic power in an aircraft is provided, the aircraft having a drivesystem comprising at least one transmission shaft connected to a powercontrol unit, the power control unit having an electric motor and ahydraulic displacement machine, both connected to a differential gearunit for driving a common output shaft. In one example, the methodcomprises hydraulic displacement machine arresting the output shaft ofthe differential gear, rotating the electric motor such that thehydraulic displacement machine is driven due to the arrested outputshaft and supplying the fluid flow into a hydraulic system. The methodaccording to the present disclosure thereby uses a hybrid PCU forgenerating hydraulic power in an aircraft.

PCUs may comprise two independent motors to provide a certain redundancyin driving the connected transmission shaft system. In the past, PCUswere mostly equipped with two hydraulic motors, while in modern hybridPCUs an electric motor and a hydraulic motor are included. In a commondesign both motors are connected to a speed summing differential gearthat has an output shaft driven by the two motors. Between each motorand a respective input shaft of the differential gear a brake issituated, which brake is released only when the respective motor isoperated. Therefore, the output shaft of the differential gear is driveneither by one of the two motors alone or by the two motors at the sametime.

The PCU is usually positioned in the fuselage of the aircraft and iselectrically connected to a computerized control, e.g. to twoindependent slat flap control computers (SFCC) for controlling andmonitoring the drive system. The output shaft of the PCU is furthermechanically connected to a transmission shaft system extending into thewings of the aircraft. The transmission shaft system thereby providesmechanical power to geared actuators at flap or slat panel drivestations distributed within the wings by means of one or moretransmission shafts.

The electric motor may be realized as a digitally controlled brushlessDC motor with a distinct reliability and efficiency. Its operation isusually established by a motor control electronic that interfaces with aslat flap control computer or any other control unit of the aircraft andan electrical bus bar. The motor control electronic thereby convertselectric power as required for the operation of the brushless DC motor.

The hydraulic displacement machine may be realized by any suitablefluidic machine that allows an operation in a pump mode and a motormode. A motor mode is necessary for operating the hydraulic displacementmachine as a motor for driving the respective input shaft of thedifferential gear unit. The hydraulic displacement machine may comprisea means for switching the operation mode from a pump mode into a motormode or vice versa, e.g. by means of a set of non-return valves allowingthe supply of pressurized hydraulic fluid to the hydraulic displacementmachine without flowing back into the hydraulic system and vice versa.In one example, the hydraulic displacement machine is an axial pistonmachine with a plurality of movably supported pistons controlled by aswivable swash plate, wherein the swash plate may be moved in twodifferent directions over a center position. This allows to vary thedisplacement of the pistons as well as the flow direction.

In the method according to the present disclosure it is assumed that thetransmission shaft is momentarily not rotated, i.e. when the high liftsystem is in a standby state. Thereby the output shaft of thedifferential gear is arrested, e.g. by means of a brake. Consequently,the two input shafts of the differential gear are coupled such that arotation of one of the input shafts leads to the rotation of the otherinput shaft, usually in an opposite direction. Once the output shaft isarrested, the hydraulic displacement machine may be driven by theelectric motor to generate hydraulic energy.

The fluid flow resulting from the rotation of the hydraulic displacementmachine is then supplied into a hydraulic system to provide hydraulicpower for hydraulic loads attached to the hydraulic system.

As the power control unit for driving slats and flaps of an aircraft isusually only operated during takeoff and landing phases, the PCU is notproviding any function in a major part of a flight mission. By combiningthe generation of hydraulic power by means of the PCU in those timeintervals that do not include any movement of slats, flaps or otherPCU-driven high lift devices, additional hydraulic power may begenerated without the necessity of operating a dedicatedpump-motor-combination. As already present components may be used forproviding an additional function thereby a clear weight advantage isachieved and dedicated pump-motor-combinations may be eliminated fromthe setup of the aircraft.

In one exemplary embodiment, arresting the output shaft comprisesarresting at least one first brake connected to the at least onetransmission shaft. By arresting the transmission shaft the output shaftis arrested as the transmission shaft is directly coupled to the outputshaft. The at least one first brake may be an already present brake ofthe transmission shaft system or an additionally integrated brake.

In another embodiment, the at least one first brake is at least one wingtip brake. In common drive systems with a PCU and a transmission shaftsystem a wing tip brake (WTB) in each wing is mechanically connected tothe transmission shaft and the wing structure for arresting and holdinga respective transmission shaft in failure cases. By activating the wingtip brakes, the transmission shaft is arrested and therefore the outputshaft of the differential gear unit, which is mechanically connected tothe transmission shaft, is arrested, too. Hence, without the necessityof any additional components the advantages of the present disclosuremay be achieved.

In one embodiment of the method, rotating the electric motor includesreleasing a second brake at the electric motor and a third brake at thehydraulic displacement machine. These brakes are usually used forpreventing the slip of one of the input shafts of the differential gearunit when exclusively the other input shaft is driven by one of themotors. In a common drive system, these brakes are automaticallyactivated when the respective motor is not driven. The second brake maythereby be realized as a power-off brake that is released once theelectric motor is powered. The third brake may be realized as apressure-off brake and may be released once the hydraulic motor ispressurized.

In case the hydraulic pressure of the hydraulic system to which thehydraulic power is to be supplied is zero, the third brake may bereleased actively, for example by a brake release unit that is capableof applying a hydraulic pressure from another hydraulic system, that isrealized as a brake release actuator or any other means.

Alternatively, the third brake may be realized as a power-off brake thatis connected to the electric motor once the PCU is operated in ahydraulic pressure generation mode.

In another exemplary embodiment, a control unit controls at least one ofthe speed of the electric motor and a displacement of the hydraulicdisplacement machine for adjusting a resulting hydraulic pressure orflow rate. In a first control method the pressure in the hydraulicsystem is controlled by adjusting the displacement of the hydraulicdisplacement machine, e.g. by adjusting the swash plate. In a secondcontrol method the displacement of the hydraulic displacement machine isfixed, e.g. to a maximum value, wherein the flow rate is controlled by acontinuous adjustment of the speed of the electric motor.

The various teachings of the present disclosure further relates to theuse of a hybrid PCU comprising an electric motor and a hydraulicdisplacement machine connected to a differential gear unit having acommon output shaft for generating hydraulic power under arresting thecommon output shaft.

In one of various embodiments, at least one wing tip brake connected toa transmission shaft system mechanically connected to the output shaftof the differential gear unit arrest the transmission shaft system forarresting the common output shaft.

A person skilled in the art can gather other characteristics andadvantages of the disclosure from the following description of exemplaryembodiments that refers to the attached drawings, wherein the describedexemplary embodiments should not be interpreted in a restrictive sense.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will hereinafter be described in conjunctionwith the following drawing figures, wherein like numerals denote likeelements, and wherein:

FIG. 1 shows a general overview of an aircraft with a drive system fordriving control surfaces.

FIG. 2 shows a part of the drive system in a schematic view.

FIG. 3 shows a simplified block-oriented schematic view of the part ofthe drive system shown in FIG. 2 in a first mode of operation.

FIG. 4 shows a hydraulic system coupled with a part of the drive systemin a schematic view in a first mode of operation.

FIG. 5 shows a simplified block-oriented schematic view of the part ofthe drive system shown in FIG. 2 in a second mode of operation.

FIG. 6 shows a hydraulic system coupled with a part of the drive systemin a schematic view in a second mode of operation.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the present disclosure or the application and usesof the present disclosure. Furthermore, there is no intention to bebound by any theory presented in the preceding background or thefollowing detailed description.

FIG. 1 shows a general overview of an aircraft 2 having a drive system 4for driving control surfaces 6 (leading edge slats) and 8 (trailing edgeflaps). The drive system 4 comprises a first transmission shaft 10located at a wing leading edge 12 as well as a second transmission shaft14 located at a wing trailing edge 16. Several drive stations 18 and 20are distributed along the leading edge 12 and the trailing edge 16,respectively. The drive stations 18 and 20 are designed for convertingrotary power into a translational movement of the control surfaces 6 and8.

The transmission shaft 10 and 14 are driven by drive units 22 and 24,exemplarily located inside the fuselage 26 of the aircraft 2. Thesedrive units 22 and 24 are usually referred to as PCU and in one example,comprise two motors, one hydraulic motor and one electric motor forproviding a hybrid operation. Two independent Slat Flap Computers (SFCC)25 may control and monitor the system.

In FIG. 2, the transmission shaft 14 arranged at the trailing edge 16 isshown in a schematic view. The PCU 24 hereby comprises a differentialgear 28 with two input shaft sections 30 and 32 to which two motors 34and 36 are coupled, each via one power-off brake 38 and 40,respectively. A power-off brake for a hydraulic motor may be apressure-off brake that is activated automatically on a loss ofpressure. The differential gear 28 may be a speed-summing differentialgear 28 that rotates a distribution gear section 42 to which twotransmission shaft sections 44 and 46 are coupled.

Drive stations 20 are distributed along the transmission shaft sections44 and are coupled to control surfaces 8. Exemplarily, two drivestations 20 are coupled to two edges of a single control surface 8 inorder to drive it. Additionally, to prevent a failure in the drivesystem in case of a shaft break or a similar event, wing tip brakes 48are arranged at end sections of the transmission shaft sections 44. Byactivating these wing tip brakes 48 the whole shaft section 44 may bearrested.

According to FIG. 2, the PCU 24 exemplarily comprises an electric motor36 and a hydraulic displacement machine 34. As shown in FIG. 3 theelectric motor 36, controlled by a motor control electronic 50, mayprovide rotational power over the power-off brake 40 into the respectiveinput shaft 32 of the differential gear 28. At the same time thehydraulic displacement machine 34 provides rotational power over thepower-off brake 38 into the respective input shaft 30 of thedifferential gear 28. This leads to the rotation of a transmissionoutput 52 of the differential gear 28. In case only one of the electricmotor 36 and the hydraulic displacement machine 34 supplies rotationalpower to the transmission output 52, the power-off brake of the othermotor, which is in a standby state, is arrested. Thereby, the respectiveinput shaft 30 or 32 is arrested such that the input of rotary powerfrom the other input shaft 30 or 32 leads to the rotation of thetransmission output 52.

As the exemplary control surfaces 6 and 8 shown in FIG. 1 are high-liftcontrol surfaces, the transmission sections 44 and 46 are poweredseldomly. Most of the time they are arrested, e.g. by the PCU itself ina high lift mode or by the wing tip brakes 48 in case the controlsurfaces are retracted or in failure cases, and are in a standby state,waiting for the next high-lift flight state. In the default high liftoperating mode the wing tip brakes 48 are released and the PCU 24 isproviding power to operate the high lift system with the commanded speedinto any gated position.

For the hydraulic displacement machine 34 a digitally controlledover-center variable displacement motor may be used. The electric motor36 may be a digitally controlled brushless DC motor. The control of themotors 34 and 36 may be established by a closed loop layout to maintainspeed and torque command inputs. The control algorithms are implementedin a controller, which is provided with all required data to control themotors. For example, the controller may be integrated in an existingcontroller of the aircraft, such as an SFCC 25.

The hydraulic displacement machine 34 is supplied by an aircrafthydraulic supply system 54, while the electric motor 36 is supplied withelectric power by an aircraft electrical busbar 51. A manifold as partof the hydraulic displacement machine 34 may be interfacing with theSFCC 25 and the hydraulic supply system 54 and contains all componentsto pressurize the hydraulic displacement machine 34 and to control therespective pressure-off brake 38.

For the electric motor 36 the motor control electronic 50 may beinterfacing with the SFCC 25 and the aircraft electrical busbar 51. Themotor control electronic 50 converts the electric power as required forthe brushless DC motor or any other type of electric motor 36.

According to FIG. 4, the electric motor 36 and the hydraulic motor 34are coupled with the differential gear 28 and power the transmissionoutput 52. The torque and hence the speed of the hydraulic displacementmachine 34, e.g. realized as an over-center variable displacementmachine, is controlled by commanding the motor swash plate into therequired position. The hydraulic power is provided by the associatedhydraulic system 54. The motor flow demand is, as part of the closedloop control algorithm, limited with the objective not to overload thehydraulic supply system 54. This requires information regarding thehydraulic pressure provided by a pressure transducer as part of ahydraulic drive channel and pressure data provided by the hydraulicsystem 54 to the motor controller. The electric motor closed loop speedcontrol is established accordingly.

The associated hydraulic system 54 is generally pressurized by enginedriven pumps 58. Additionally the hydraulic system 54 is usuallyequipped with electric motor pumps 56 to provide the hydraulic power incase the engine driven pumps are not active, e.g. in a ground or failurecase, or to increase the power of the hydraulic system in case of highflow demand. Besides that, filters 60, check valves 62 and 64 andconnecting sections 66 for the integration of other hydraulic loads 68are present for filtering hydraulic fluid and for assigning flowdirections.

As indicated above and shown in FIG. 5, electric power may be convertedinto hydraulic power by simply arresting the transmission output 52 androtating the electric motor 36 such that the hydraulic displacementmachine 34 rotates in an opposite direction through the differentialgear 28. Generally, the objective is to use a hybrid PCU of a high liftsystem also as an electric motor pump within the aircraft hydraulicsupply system 54. A hybrid PCU, equipped with a digital controlledover-center variable displacement hydraulic displacement machine 34 andan electric motor 36 coupled via a differential gear 28, comprises allfeatures required for an electric motor pump to pressurize the aircrafthydraulic system 54. To operate the hybrid PCU in an electric motor pumpmode the transmission output 52 of the differential gear 28 is locked byengagement of the wing tip brakes 48 as first brakes. The power-offbrakes 38 and 40 as second and third brakes associated to each motor 34and 36 are released by corresponding command inputs, e.g. by the SFCC25. This provides power flow from the electric motor 36 to the hydraulicdisplacement machine 34 via the differential gear 28. In thisconfiguration the high lift system is safely fixed by the wing tipbrakes 48. After operation of the PCU 24 as an electric motor pump thereaction torque in the transmission is relieved by a correspondingsequence already implemented for the high lift application.

This is further depicted in FIG. 6 where the transmission output 52 isarrested and the hydraulic displacement machine 34 is driven androtates. Due to the rotation, a hydraulic pressure is generated and fedinto the hydraulic system 54. By controlling the hydraulic motor 34,e.g. through a controller interface 70 connected to the SFCC 25 or anyother control logic, the generated pressure as well as the generatedvolume flow is controllable.

Alternatively the pump performance can be controlled by adjusting thespeed of the electric motor 36 depending on the required flow tomaintain the hydraulic system pressure. In this case the pumpdisplacement is controlled and maintained into a fixed position by thespring loaded swash plate actuation mechanism and corresponding commandinput from the controller.

Generally, a swash plate actuation mechanism of the hydraulic motor 34,e.g. in form of an over-center hydraulic drive, is spring loaded toprovide an initial pump displacement for start-up when the hydraulicsystem 54 is not yet pressurized. The electric motor 36 is commanded toa desired speed, in one example, by the SFCC or any other controller.The electric motor 36 is now powering the hydraulic motor 34 via thedifferential gear 28. In consequence of the initial swash displacementthe hydraulic motor 34 is operating in a pump mode and is pressurizingthe hydraulic system 54. The hydraulic interface to the PCU is adaptedto the needs for a hydraulic pump.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of thepresent disclosure in any way. Rather, the foregoing detaileddescription will provide those skilled in the art with a convenient roadmap for implementing an exemplary embodiment, it being understood thatvarious changes may be made in the function and arrangement of elementsdescribed in an exemplary embodiment without departing from the scope ofthe present disclosure as set forth in the appended claims and theirlegal equivalents.

1. A method for generating hydraulic power in an aircraft, the aircrafthaving a drive system comprising at least one transmission shaftconnected to a hybrid power control unit, the power control unit havingan electric motor and a hydraulic displacement machine connected to adifferential gear unit for driving a common output shaft, the methodcomprising: arresting the output shaft; rotating the electric motor suchthat the hydraulic displacement machine is driven due to the arrestedoutput shaft; and supplying the fluid flow into a hydraulic system. 2.The method of claim 1, wherein arresting the output shaft comprisesarresting at least one first brake connected to the at least onetransmission shaft.
 3. The method of claim 2, wherein the at least onefirst brake is at least one wing tip brake.
 4. The method of claim 1,wherein rotating the electric motor includes releasing a second brake atthe hydraulic displacement machine and a third brake at the electricmotor.
 5. The method of claim 4, wherein the second brake is apressure-off brake and wherein releasing the second brake includesdriving a brake release unit coupled with the pressure-off brake torelease the pressure-off brake in case the corresponding hydraulicsystem is not pressurized.
 6. The method of claim 1, wherein a controlunit controls at least one of the speed of the electric motor and adisplacement of the hydraulic displacement machine for adjusting aresulting hydraulic pressure or flow rate.
 7. An aircraft, comprising:an electric motor; and a hydraulic displacement machine coupled to adifferential gear unit having a common output shaft for generatinghydraulic power under arresting the common output shaft and rotating theelectric motor.
 8. The aircraft of claim 7, wherein at least one wingtip brake of the aircraft connected to a transmission shaft mechanicallyconnected to the output shaft of the differential gear unit forarresting the transmission shaft is used for arresting the common outputshaft.
 9. A drive system for moving at least one control surface of anaircraft and for generating hydraulic power in an aircraft, comprising:at least one transmission shaft connected to a hybrid power controlunit, the power control unit having an electric motor and a hydraulicdisplacement machine coupled to a differential gear unit for driving acommon output shaft, wherein the drive system is adapted for arrestingthe output shaft such that by rotating the electric motor the hydraulicdisplacement machine is driven due to the arrested output shaft andsupplies the fluid flow into a hydraulic system.
 10. The drive system ofclaim 9, wherein the drive system arrests at least one first brakeconnected to the at least one transmission shaft.
 11. The drive systemof claim 10, wherein the at least one first brake is at least one wingtip brake.
 12. The drive system of claim 9, further comprising a controlunit that controls at least one of the speed of the electric motor and adisplacement of the hydraulic displacement machine for adjusting aresulting hydraulic flow rate.